Each mobile app will be pre-allocated 25 numbers whether it's invoice number, job number, or quote number. This is to make sure that a mobile app user is able to create a job, create an invoice, or create a quote even without mobile coverage as Ascora supports offline mode.
You will see a jump in numbers and this won't be an issue and it's the expected behaviour to guarantee unique job numbers, invoice numbers, or quote numbers can be allocated. You might see a big gap when mobile apps are being deleted and reinstalled multiple times.